Question about measured values (esp. 18 & 19) of my recent G3-Blues build!

  • Hi Martin,

    In accordance with Klaus (MD) he suggested it would be best to consult you about my recent G3-Blues (a nice gesture for all of us before posting a review/my findings on the MD-website).

    Briefly, from a socalled 'far-away-friend' I heard about MD and he told me about his G3-Rock version. Indeed, a nice and affordable package to be purchased at MD. So I proposed to contact him after the construction in order to compare (soundwise) my G3-Blues I had purchased a few months ago with his G3-Rock (because I prefer a more clean sound, that's why).

    After construction, first I checked and recheckedthe whole system. No smoke or explosions :evil::saint: . But I heard just an increasing hum when approaching with the multimeters' pins.

    Upon measuring my amp, I noticed most of the values were within a loose 10%. Everything seemed to be quite normal (within these limits), but on 'V2-6' position I noticed a somewhat different value 124 Volts (in stead of the given 166 Volts). However, measuring a bit further became more weird (in my humble opinion). At the last two measuring points [18 & 19] these both voltages seemed to be around 'zero' (I checked all components over and over again). Weird it is 🤔😰. Note that the measurements of my friends' G3-Rock were all in a tight 1-2 %.

    Soundwise, I also compared my Blues with the Rock-version. It was strange to discover that my G3 sounded much louder (even at extremely low 'seven 'o clock position'; almost 'zero'). Also, the influence of the Tone-dept was more pronounced in my Blues-version. In other words, dialing up the [Bass-]-EQ on the Rock hardly gave any difference in the low end. But my Blues-version already had more low end in itself (!). We 'exchanged' cabinets by crossing our both speaker connections 🤗; with more or less the same results (in terms of differences in sound and volume). By the way, the Gain-potmeter on my Blues hasn't the same 'dramatic' influence as on the Rock-version (but that seems not very surprising to me).

    Until now, everything sounds right (at least, as far as I can tell) although the mentioned measurements indicate a different story. Do I have a problem here or is it a common finding?

    Hope to hear from you, because this self-constructed little amp seems very nice to me 8o .


    Thanks and musical greetings,

    Bram Backx

    Oegstgeest - NL

    Note: At first No Sound was detected. The first V-I Tube didn't glow. But I checked all the leads and resoldered some of them. With the expected good results. The tube seemed to be okay, but there was a poor soldered lead (although I developed these skills almost 25 years ago, I cpuld just blame myself for it). Nevertheless, a good learning moment for me...

  • Hi Bram,

    those two voltages around 0V are very strange, you‘re measuring DC voltage to ground, right? You‘re measuring 50v DC at V2-3, but no voltage at the other end of R15? With the amp switched off and V2 removed please measure the resistance of R13, R15 and R16. And at V3-3/8 there has to be around 10V DC, otherwise the Bias of V3 is completely wrong and the tube will be damaged shortly…

  • Hi there Martin,

    Thank you for your quick response. Of course, I checked and rechecked every part during the last week (= meaning twice 🤗).

    I also switched all the tubes (I already ordered a set of spare tubes) which didn't make much difference.

    Anyway, the 10-b Lug shows a healthy 46 Volt (of course in DC; otherwise my multimeter begins to 'bleep' 😏). You wrote R15, abusively but I think you just meant R13 of course. No problem. However, the V3-3+8 measurement still remains around zero whereas measuring a bit further 'in the chain', say at Lug-14 'Up and Down' (unten) I still measured a healthy 10.71 Volt (the positive red at the respective lugs, the black pointer stays firm at 'cental ground connection'; in DC-mode).

    Furthermore I still noticed an increasing 'hum & noise' when litterally approaching the enclosure, esp. in the V2-area. By hand! As if it is some kind of Theremin-device 😎. But maybe, I already detected a minor problem. It seems that the Vol-potmeter is broken from start ('kaput' as you Germans then say). Bcause these parts look so very solid, I assumed that they were all good. Whereas the other four show expected values, this one didn't show 1 MOhm, but still remained around a poor 4 Ohm. So this could explain why my G3-Blues version sounded so extremely loud (when compared with my friends' G3-Rock version... Maybe this will also explain all the problems (microphonic behaviour?) at the V2-area?! Especially at the V2-6 point, which still remains around ±120 Volts instead of the recommended 166 Volt. Note that most values are in a loose 10 % or less margin.

    Could this also explain the trouble at the V3-3+8 measuring point?

    In the meanwhile I continue my research. If you have some useful suggestions, I am more than willing to be informed. As I'm no electrician and not really able to 'read' these schematics. For me it is more a very precise procedure 'do this & do that' 😇.

    Thank you and quiet holydays, fröhliche Weihnachten, gesund 2022 usw.

    Bram Backx

    Oegstgeest - NL

  • Bram, I highly recommend to make yourself familiar with the schematic, otherwise it will be complicated to determine the problem itself. Most of us experienced builders are also a bit reluctant to provide support here to someone not able and/or willing to use the schematic because it needs a lot more explanation and work to help w/o that.

    Two examples: I wrote R15 and I meant R15 => as you can see in the schematic, R13 + R15 + R16 are connected to each other so there has to be the same voltage of 47V DC at them.

    Secondly, you say that the resistance of the Volume pot is about 0 ohm => if you measure between input and output of that pot fully turned clockwise there has to be about 0 ohm, if you measure between output and ground of the pot fully turned clockwise with treble/bass/mid fully turned anti-clockwise you also will measure 0 ohm as you can see from the schematic. So i doubt that the pot is broken, they rarely break and if so, they typically have infinite resistance.

    So my advice is a) make yourself familiar with the schematic to understand which values you can expect when measuring e.g. resistance in the circuit and b) focus first on the missing bias voltage (about 10V DC at pins 3 and 8 of V3), this is the major reason that your amp doesn't work and as said it might destroy V3 on medium term...

  • Davide Violante

    Rockers&&Rocks

    http://www.rockers.rocks

    Schoonenburgsingel 176

    2135GE Hooffdorp

    Netherlands

  • Dear Hendrixianer,

    You are not in the needs to judge as I didn't say something bad here I only mentioned the truth. We can't say that the forum is made for helping people with building an amp, the forum is made for discussions, you too mentioned that.

    So it is ok like that, but this is not the same meaning of other forums, that is my only point.

    We can't say that Madamp use the best components as this is not true and obviously is cheap Amp a lot cheaper and for a reason. this is expected no problem

    The other issue is this is not beginners project not with the instructions provided because instructions sucks that is 100% sure.

    Davide Violante

    Rockers&&Rocks

    http://www.rockers.rocks

    Schoonenburgsingel 176

    2135GE Hooffdorp

    Netherlands

  • Davide,

    how can you judge on a documentation you've never seen? Both G3 kits are entry level kits with detailed documentation and >100 of them have been built successfully following the manual.

    And you're wrong, this is a support forum for MADAMP kits (that's why I'm answering all support requests and questions not answered by other members of this forum). You're free to post your view and experience regarding your M15 built, but please stop generalizing w/o facts.

  • Davide Violante

    Rockers&&Rocks

    http://www.rockers.rocks

    Schoonenburgsingel 176

    2135GE Hooffdorp

    Netherlands

  • Hi there Martin (this message is meant 'for your eyes only'),

    First of all, I must apologize for the indulging and condescending attitude of my 'fellow countryman' towards socalled 'beginners' on this Forum. Klaus from MD advised me to contact you (about my G3-Blues). Of course I'm more than willing to get some useful advice from YOU (and you only).

    By the way, a certain kind of Dutch persons feel the need to ventilate their unsolicited opinion all the time (as if they were the utmost expert). For example, when there is a Football World Championship those people turn themselves into 'national coaches' (approximately 18 milljon all over the country). and do think we already won the challenge from the start. Something like that. When there is a pandemia they turn themselves in a 'virologist'. Catch my drift..?!

    So let me first establish that he doesn't know exactly who I am and what I stand for. Of course not! But now I'm convinced he needed to egoboost himself by placing himself above others with (assumed) lesser skills. Well anyway, in the field of social skills hé still remains an absolute beginner :* <X .

    If this 'violent words' person Violante really want to 'help' people; go to a refugee-camp! So please. let me discover my hobby with all the expected pitfalls (I already know I'm no professional; so what's the point?!). This is not an elite society, just for people with abundant and demonstrable skills. But a forum for real musicians with maybe clumsy but realistic and honest questions. Happily Martin is willing to answer as far as possible. I really appreciate that. End of this stupid debate.

    Let us continue with the more realistic and practical problem. Meanwhile I adressed the problem of the A1M-potmeter. Admitted, it wasn't broke or so, but I accidently exchanged two yellow leads. Meaning the centre of V2 and Lug-4 (under) thus resulting in some weird 'short-cut'?! Yep, indeed it was 'clumsy'. But it's not my job, so no world shocking disaster (I discovered it myself, which is always the best lesson). The measuriements seem to be okay now.

    It's not true to state that I am 'reluctant' to consult the schematics. I hope you understand that for people without any electronic skills or education it is reading like a foreign language: I do recognize some words, but the meaning of the whole sentence still remains unclear (no matter how much I try to study it. Indeed, if someone would be so helpful to explain it to me...). Having said this, maybe it is good to mention that I already constructed the G3-Rock version myself about a year ago. I fixed it without any failure, just consulting the Manual and the nice Wiring Diagram. I also constructed a few other projects by carefully mounting all the specific parts at the right place. Moreover I also combined two FX-kits in one BBDD-enclosure. It worked perfectly from the start. Not based on complex schematics, but on my feeling of logical constructions. So, it is not true to state I'm just a beginner...

    My last problem still remains at the V3-[3+8] points. Briefly, when I measure these (3) & (8) points with the [Red]-pointer and keep the [Black] one at an earth-point I constantly measure somewhere around 11,72 V. Even when descending to the upper Lugs 14 & 15 I still measure the same ±12 V.

    However, when using both pointers at respectively V3 at (3) and (8) my Volt-meter shows a value around zero (0 Volts). Is that the right or wrong conclusion (because my G3-Rock still works fine...)? Well, I hope to hear from you. For now, I wish you (all) a healthy and musical 2022. Greetings,

    Bram Backx

  • Hi Bram,

    as shown in the schematic (that's why I strongly recommend to make yourself familiar with it) pins 3+8 of V3 are connected, so there should be no measurable voltage between them but the DC voltage to ground across the resistors as shown in the schematic. Your voltage is a bit higher (11,7V against 10,5V) but still OK.

  • Davide Violante

    Rockers&&Rocks

    http://www.rockers.rocks

    Schoonenburgsingel 176

    2135GE Hooffdorp

    Netherlands

  • Hi there Martin, thank you for reassurance. I certainly try to study upon the schematics. It is no 'reluctance' or 'arrogancy'. It is more like staring at Chinese of Russian language (and hopefully recognizing, understanding one word of it 🤗). But anyway, thank you for your advice. So finally, my G3 Blues is still allowed and able to get the Blues out of it?! Let's rock & roll... 😎.

    At last but not least a little comment about the enclosure itself. It appeared that the welding in the corners wasn't carried out very securely. At two corners they came a bit loose or something. However, with a bit of extra care everything works fine now.

    Next summer I will consider purchasing a second G3 Blues. Just for fun of constructing and indeed, to study in more detail the schematics step-by-step. And consider that most customers of MD are musicians (at least that is what I assume) and no highly educated electrotechnicians. To be honest, I never thought I was able to 'construct' a tube-amp myself. So thank you that you brought this elegant design to 'the common people'. Musical greetings,

    Bram Backx

    Oegstgeest - NL

  • Hi Bram,

    Congrats to your first amp build! :thumbup:

    If you like more Rock'n'Roll, than you might take a look at the G3 Blues' meaner brother, the G3 Rock. Just as easy to build and it sounds fantastic. :)

    If you are interested in learning something more about amp circuitry, here are some very helpful links:

    http://www.valvewizard.co.uk

    How Amps Work

    Amp Books Tutorials

    Enjoy, have fun, take care and stay healthy brother!

    Max <3

    "Perfektion ist nicht dann erreicht, wenn es nichts mehr hinzuzufügen gibt, sondern wenn man nichts mehr weglassen kann."
    - Antoine de Saint-Exupéry

Jetzt mitmachen!

Sie haben noch kein Benutzerkonto auf unserer Seite? Registrieren Sie sich kostenlos und nehmen Sie an unserer Community teil!